For-loop produces a redundant BLOCK

[Synix4Life]

Description

When using a for loop, the Kongruent intermediate representation generates a redundant BLOCK. This block encapsulates both the loop condition variable (if defined in the for statement) and the while loop, even though the while loop already forms a block (WHILE_START -> WHILE_END).

Example

Given the shader.kong code:

var sum: float = 0.0;
for (var i: float = 0.0; i < 4.0; i = i + 1.0) {
        ...
}
return sum

This results in the IR code:

$84 = LOAD_FLOAT_CONSTANT 0.000000   // float sum
$83 = STORE_VARIABLE $84

BLOCK_START [ID: $86]   // Redundant Block (Start)

    $88 = LOAD_FLOAT_CONSTANT 0.000000  // float i
    $85 = STORE_VARIABLE $88 

    WHILE_START [ID: $89] -> BLOCK [start=$89, continue=$90, end=$91]   // While Block (Start)

        $92 = LOAD_FLOAT_CONSTANT 4.000000 
        $93 = LESS $85, $92 

        WHILE_COND $93   

        BLOCK_START [ID: $94]   // Loop Body Block (Start)
                 ...
        BLOCK_END [ID: $95]   // Loop Body Block (End)

    WHILE_END [ID: $91] -> BLOCK [start=$89, continue=$90, end=$91]   // While Block (End)

BLOCK_END [ID: $87]   // Redundant Block (End)

RETURN $83
...

In the example above, the statements $88 = LOAD_FLOAT_CONSTANT 0.000000 and $85 = STORE_VARIABLE $88 can be moved out of BLOCK $86, as they are either way only executed once. This results in the sequence

BLOCK START
WHILE START (aka. BLOCK  START)
...
WHILE END (aka. BLOCK END)
BLOCK END

, i.e. two blocks of which one is unnecessary.